A HYDROGEN-1, CARBON-13, AND NITROGEN-15 NUCLEAR MAGNETIC RESONANCE STUDY OF p-BENZOQUINONE POLYMERS INCORPORATING AMINO NITROGEN COMPOUNDS (“SYNTHETIC HUMIC ACIDS”)

Abstract

We made a chemical and NMR study of a set of phenolic polymers of the type long proposed as possible synthetic models for humic acid. Twelve polymers were prepared by air oxidation of p-benzoquinone, and p-benzoquinone plus ammonium chloride, glycine, diglycine, triglycine, alanine, dialanine, alanylglycine, glycylalanine, casein, casein hydrolyzate, and 95 percent 15]N-enriched ammonium chloride. These were characterized by elemental and functional group analysis, acid hydrolysis, dialysis, infrared spectroscopy, and 1]H, 13]C, and solid-state CPMAS 13]C NMR spectroscopy, and by 15]N NMR of the 15]N-enriched polymer. The results strongly support previous suggestions that the polymers are formed by coupling of semiquinone radicals generated in solution, giving a hydroquinone-type skeleton, that amino compounds may be incorporated by formation of bonds between amino nitrogen and aromatic carbon, and that some decarboxylation and deamination of amino acids occurs during polymerization. In addition, formation of carboxylic acid groups and an aliphatic component for all polymers suggests that some ring-opening occurs during polymerization. There was also possible evidence for formation of amides in the nitrogen-containing polymers. We made a chemical and NMR study of a set of phenolic polymers of the type long proposed as possible synthetic models for humic acid. Twelve polymers were prepared by air oxidation of p-benzoquinone, and p-benzoquinone plus ammonium chloride, glycine, diglycine, triglycine, alanine, dialanine, alanylglycine, glycylalanine, casein, casein hydrolyzate, and 95 percent 15]N-enriched ammonium chloride. These were characterized by elemental and functional group analysis, acid hydrolysis, dialysis, infrared spectroscopy, and 1]H, 13]C, and solid-state CPMAS 13]C NMR spectroscopy, and by 15]N NMR of the 15]N-enriched polymer. The results strongly support previous suggestions that the polymers are formed by coupling of semiquinone radicals generated in solution, giving a hydroquinone-type skeleton, that amino compounds may be incorporated by formation of bonds between amino nitrogen and aromatic carbon, and that some decarboxylation and deamination of amino acids occurs during polymerization. In addition, formation of carboxylic acid groups and an aliphatic component for all polymers suggests that some ring-opening occurs during polymerization. There was also possible evidence for formation of amides in the nitrogen-containing polymers. © Williams & Wilkins 1982. All Rights Reserved.